EP0695583A1

EP0695583A1 - Powder paint supply device

Info

Publication number: EP0695583A1
Application number: EP95112383A
Authority: EP
Inventors: Haruhisa Kaiju; Akihisa Yoshizaki; Junichi Yukikawa; Hitoshi Yoshida
Original assignee: Matsuo Sangyo Co Ltd
Current assignee: Matsuo Sangyo Co Ltd
Priority date: 1990-12-27
Filing date: 1991-12-20
Publication date: 1996-02-07
Anticipated expiration: 2011-12-20
Also published as: ES2083537T3; DE69132062D1; EP0496165A2; DE69132062T2; DE69117275D1; EP0496165A3; EP0695583B1; US5240185A; US5335828A; DE69117275T2; US5323547A; EP0496165B1

Abstract

A fluidized type powder paint tank 51 having a fluidizing chamber 2 for fluidizing a powder paint and a storage chamber 3 into which the powder paint in the fluidizing chamber is fed to keep it still. There is also provided a paint supply device for an electrostatic powder painting device having a paint tank 51 for containing a powder paint and a painting gun 82 coupled to the paint tank through an injector 78 and a hose 81. This device further includes a discharge device 54 for discharging the powder paint out of the paint tank 51 and a hopper 55 for receiving the powder paint discharged by the discharge device. A screw feeder 58 is provided in the hopper. With this arrangement, the powder paint supplied at a uniform rate from the screw feeder is fed into the injector.

Description

This invention relates to an improved powder paint supply device in an electrostatic powder painting device and extending from a powder paint tank to a painting gun and adapted to achieve a uniform discharge of powder paint through the painting gun and thus to obtain a painted surface having a uniform paint film thickness.
A conventional powder paint supply device had various problems. First, the powder paint tank has the following problems. Heretofore, as the tank for an electrostatic powder paint device, a fluidized type powder paint tank has been used.
In case of such a powder paint tank, a porous resin plate is provided on the bottom of the tank. Compressed air is supplied into the tank through the porous resin plate to stir and dehumidify the powder paint in the tank. The density of the powder paint in the tank changes with its amount in the tank.
For example, as the amount of powder paint in the tank decreases, i.e. the powder paint level in the tank lowers, the density of the powder paint decreases correspondingly.
Thus, if the powder paint in the fluidized type powder tank is drawn out by a discharge device such as an injector, the discharge rate changes according to the powder paint level in the tank as shown by line a in Fig. 1.
Thus, it was impossible with such a conventional fluid type powder paint tank to discharge the powder paint at a unform rate.
It is therefore a first object of the present invention to provide a fluidized type powder paint tank which can discharge powder paint at a uniform rate without being affected by the powder paint level in the tank.
Secondly, there have been the following problems in drawing out the powder paint out of the powder paint tank. As a conventional device for drawing the powder paint out of the powder paint tank, there is known one comprising a discharge pipe provided at the lower part of the powder paint tank and a pinch valve attached to the discharge pipe and adapted to close the flow line by supplying air. The powder paint in the powder paint tank can be discharged by opening and closing the pinch valve.
In case of this type of device, if the discharge of powder paint is stopped for a long time by closing the pinch valve, the powder paint left in the discharge pipe at its part over the pinch valve may become humid so that the discharge pipe may be clogged with the powder paint at that part. This makes it difficult to drop the powder paint smoothly by opening the pinch valve and thus to supply the powder paint smoothly.
A second object of the present invention is to provide a powder paint discharge device which prevents the discharge pipe from getting clogged with powder paint and thus can assure smooth discharge of the powder paint in the tank.
Thirdly, a paint supply device for supplying the powder paint in the powder paint tank to the painting gun had the following problems.
In case of a conventional paint supply device, an injector is directly attached to the side or top of the paint tank containing powder paint. The injector is coupled to the painting gun through a hose. The powder paint in the paint tank is drawn out by the injector together with air. The air is used to send the powder paint to the painting gun.
The discharge rate through the painting gun is determined by the air pressure and air amount of the injector. In order to provide a painted surface having a uniform film thickness, the discharge rate through the painting gun has to be uniform.
But even if the air pressure and air amount of the injector are unchanged, when the amount of powder paint in the paint tank decreases, the air content in the powder paint increases and the pressure changes according to the layer thickness of the powder paint, so that the amount of powder paint sucked by the injector decreases. This in turn causes decrease in the discharge rate of the powder paint through the painting gun. Thus, it was difficult to form a paint film having a uniform thickness. This may result in transparent paint films or defective painted goods.
If powder paint sticks to the inner surface of the hose extending from the injector to the painting gun or if the hose is clogged with foreign matter, pressure loss will occur in the hose. This reduces the amount of paint sucked into the injector, thus changing the discharge rate of powder paint through the painting gun.
Thus, in case of a conventional paint supply device having an injector attached to the paint tank to directly suck the powder paint in the paint tank, it was difficult to discharge the powder paint through the painting gun at a uniform rate.
A third object of the present invention is to provide a powder paint supply device which assures a uniform discharge rate of powder paint through the painting gun.
Other features and objects of the present invention will become apparent from the following description taken with reference to the accompanying drawings, in which:

Fig. 1 is a graph showing the relation between the level of the paint in the tank and the discharge rate;
Figs. 2 - 6 are schematic side views of preferred embodiments of the powder paint tank according to this invention;
Fig. 7 is a sectional view of the outlet portion of an embodiment of the powder paint tank according to the present invention;
Fig. 8 is a side view of Fig. 7;
Fig. 9 is an entire view of the powder paint supply device according to this invention;
Fig. 10 is a sectional view of a portion of the device of Fig. 9; and
Fig. 11 is a partial enlarged view of a portion of Fig. 10.

In order to solve the first problem, this invention provides an improved fluid type powder paint tank. Its embodiments are described with reference to Figs. 2 - 6.
The fluidized type powder paint tank 1 according to this invention has a fluidizing chamber 2 for moving powder paint A as a fluid and a storage chamber 3 for holding the powder paint A drawn from the fluidizing chamber 2 in a stationary state.
A discharge device 4 is attached to the storage chamber 3 to discharge the powder paint A therefrom. The powder paint tank of the embodiment shown in Figs. 2 and 3 is provided with a partitioning wall 5 on the righthand side thereof, defining the fluidizing chamber 2 on the left of the wall 5 and the storage chamber 3 on its right.
In the fluidising chamber 2 at the lower part thereof, a porous plate 6 is provided slightly spaced apart from the bottom thereof. Compressed air 7 is fed under the porous plate 6. An air vent 8 is provided at the top of the fluidizing chamber 2.
The fluidizing chamber 2 and the storage chamber 3 communicate with each other at the lower part of the fluidizing chamber 2. An air purge nozzle 9 is provided in the fluidizing chamber 2 at the lower part thereof to discharge the powder paint A in the fluidizing chamber 2 into the storage chamber 3 by intermittently feeding air toward the storage chamber 3. Instead of the air purge nozzle 9, the powder paint A in the fluidizing chamber 2 may be discharged into the storage chamber 3 with a scraper which moves on and along the porous plate 6 toward the storage chamber 3,
The bottom of the storage chamber 3 is at a level lower than the bottoms of the porous plate 6 and the tank 1.
An injector as the discharge device 4 is mounted at the lower part of the storage chamber 3. A painting gun 11 is connected to the injector 4 through a powder supply hose 10.
The embodiment shown in Fig. 4 has the same structure as the embodiment shown in Figs. 2 and 3 except the discharge device 4.
The discharge device 4 in this embodiment has the following structure. Namely, a screw 13 rotated by a motor 12 is mounted in the bottom of the storage chamber 3. A discharge port 14 is formed in the side of the storage chamber 3 at the front end of the screw 13. Beside the discharge port 14, there is provided a cylindrical flow straightener 15 having a drop hole in the bottom thereof. Beside the flow straightener 15, a spring housing 16 is provided. A lid plate 18 is secured to the end of the screw 13 and pressed against the discharge port 14 by a spring 17 housed in the spring housing 16.
By rotating the screw 13 with the motor 12, the powder A at the bottom of the storage chamber 3 is pushed out toward the discharge port 14. The spring 17 is compressed and the lid plate 18 is opened by this pushing force, so that the powder is blown out through a gap between the lid plate 18 and the discharge port 14. The powder thus blown out hits and moves along the inner peripheral surface of the flow straightener 15 and is discharged in uniform amounts into a hopper 19 provided thereunder. An injector 20 is mounted to the bottom of the hopper 19. The powder is fed from the injector 20 into the painting gun 11 through a powder supply hose 10.
In the embodiment shown in Fig. 5, a porous plate 6 is provided over the bottom of the tank 1 so as to cover the entire bottom surface. A partitioning wall 5 is provided to divide the space over the porous plate 6 into the fluidizing chamber 2 and the storage chamber 3. A shield plate 21 is provided on the porous plate 6 at its portion located in the storage chamber 3 near its bottom to prevent the air supply from the porous plate into the storage chamber 3. Otherwise, the embodiment shown in Fig. 4 is the same in structure as the embodiment shown in Fig. 1.
The tank 1 of the embodiment shown in Fig. 6 has the same structure as that of the embodiment shown in Fig. 5. The discharge device 4 has the same structure as that of the embodiment shown in Fig. 4. In the embodiment shown Fig. 6, the motor 12 for the screw 13 is mounted on the tip of the screw.
The powder paint tank according to this invention can discharge the paint in constant amounts irrespective of the paint level in the tank. Thus, the thickness of paint can be kept constant.
In order to solve the second problem, this invention provides an improved means for drawing out a powder paint. Its embodiment is described with reference to Figs. 7 and 8.
In a powder paint tank 31, a porous plate 32 is mounted in the tank at the bottom thereof. Compressed air is supplied under the porous plate 32 to move the powder paint in the tank.
An outlet port 33 is formed in the side wall of the tank 31 at its lower part. An outlet pipe 34 is connected to the outlet port 33.
A pinch valve 35 is connected to the bottom end of the outlet pipe 34. It comprises a shrinkable tube 36 made of rubber or the like and a casing 37 covering the tube 36. An air supply pipe 38 is connected to the casing 37. By supplying air through the air supply pipe 38 into between the inner wall of the casing 37 and the outer wall of the tube 36, the tube shrinks, thus closing the flow path. When the supply of air is stopped, the tube 36 expands, opening the flow path.
The air supply pipe 38 has a branch pipe 39 connected to the outlet pipe 34 above the pinch valve 35. In the branch pipe 39 is provided a check valve 40 to prohibit the fluid flow from the outlet pipe 39 toward the air supply pipe 38.
When the pinch valve 35 is closed by supplying air into the air supply pipe 38 of the pinch valve 35, the air is also supplied through the branch pipe 39 into the outlet pipe 34 over the pinch valve 35. Thus, while the pinch valve 35 is closed, the powder paint in the outlet pipe 34 is continuously moved by the air supplied. This prevents the clogging of the outlet pipe 34.
When the pinch valve 35 is opened by stopping the supply of air into the air supply pipe 38, the supply of air into the outlet pipe 34 through the branch pipe 39 is also stopped. Thus, the powder paint in the powder paint tank 1 is drawn out downwards through the outlet pipe 34 and the pinch valve 35.
The powder paint drawn out through the pinch valve 35 is supplied into the painting gun through a hopper 41.
According to this invention, even if the drawing of the powder paint is stopped for a long time by shutting the pinch valve 35, the outlet pipe 34 will never clog. Thus, when the pinch valve 35 is opened to resume drawing the powder paint, it can be drawn out smoothly.
Even if no air is supplied through the porous plate 32 provided at the bottom of the powder paint tank 31 while not in operation, air is supplied into the powder paint tank 31 through the outlet pipe 34. Thus, the powder paint in the powder paint tank can be stirred by this air flow even while not in operation.
In order to solve the third problem, this invention provides an improved powder paint supply device for supplying a powder paint from the powder paint tank into the painting gun. Its embodiment is described with reference to Figs. 9 - 11.
A powder paint tank 51 is of a fluidized type. In this type of powder paint tank, in order to improve the dispersibility of the powder paint, air is uniformly blown into the powder layer through a porous plate 52 provided at the bottom to fluidize the powder paint.
To the lower part of the paint tank 51 is connected a discharge pipe 54 provided with a pinch valve 53. By opening the pinch valve 53, the powder paint in the powder paint tank 51 can be discharged downward by free fall.
The discharge pipe 54 is connected to the top of a hopper 55, which is provided with a level switch 56 for detecting the level of the powder paint stored in the hopper. The hopper 55 is provided with a lid 57 on top thereof. The lid 57 is provided with an air vent to expel excess air present in the powder paint fed into the hopper 55. Thus, the amount of the paint in the hopper 55 per unit volume will be uniform.
Under the hopper 55 is provided a screw feeder 58 for feeding powder. The screw feeder 58 has a screw 59 having its tip protruding into a discharge port 60 formed in the side of the hopper 55 near its bottom. The rear end of the screw 59 protrudes out of the hopper 55 and coupled to a motor 62 through a joint 61. Adjacent the discharge port 60, there is provided a cylindrical flow straightener 63. Adjacent the flow straightener 63, there is provided a spring housing chamber 65.
To the tip of the screw 59 is coupled a support shaft 66 extending through the flow straightener 63 and the spring housing 65. A lid plate 67 is slidably fitted on the support shaft 66 at its portion located in the flow straightener 63 to close the end face of the discharge port 60. Further, a pipe 68 is fitted on the support shaft 66 at its portion behind the lid plate 67. The pipe 68 has its tip end protruding into the spring housing 65 and its rear end secured to the back of the lid plate 67. A spring 69 is fitted on the support shaft 66 at its portion located in the spring housing 65. The lid plate 67 is pressed by the spring 69 through the pipe 68 against the discharge port 60.
A support plate 70 for supporting the end of the spring 69 is mounted on the tip of the support shaft 66 so as to be movable relative to the support shaft. In order to adjust the force of the spring 69, the support plate 70 is moved by turning a threaded cap 85 provided at the end of the spring housing 65.
An air inlet pipe 71 is connected to the spring housing 65. Its interior is kept at positive pressure, thus preventing powder paint from flowing into the spring housing 65.
An agitating rotary wheel 72 is mounted in the hopper 55 at its lower part, It is provided around its periphery with protrusions 73 at predetermined intervals so that they can fit into the pitch gaps defined by the screw 59. Thus, the agitating rotary wheel 72 is adapted to rotate as the screw 59 turns.
A damper plate 74 is provided in a drop port 64 of the flow straightener 63. By changing the angle of the damper plate 74, the size of the drop port 64 can be changed. Thus, even when supplying a small amount of powder paint, the powder paint is prevented from being scattered. The screw feeder 58 is detachably mounted in the hopper 55. Further, the screw 59 of the screw feeder 58 and a casing 75 are replaceable.
As the screw 59 is rotated by the motor 62, the powder paint forming the lower layer in the hopper 55 is pushed out toward the discharge port 60. By this pushing force, the spring 69 is compressed and the lid plate 67 is opened, so that the powder paint pushed out through a gap between the lid plate 67 and the discharge port 60 will blow out. The powder paint blown out of the lid plate 67 and the discharge port 60 then hits the inner surface of the flow straightener 63 and is discharged at a constant rate through the drop port 64 while moving along the inner peripheral surface of the flow straightener 63.
A chute 76 (Fig. 9) is provided under the drop port 64 of the flow straightener 63. To an outlet 77 of the chute 76 is coupled an inlet port 79 of an injector 78. A hose 81 is coupled to a discharge port 80 of the injector 78. A painting gun 82 is coupled to the tip of the hose 81. A sensor 83 is provided in the chute 76 which is adapted to detect a predetermined amount of powder paint. The amount of air to be fed into the injector 78 will be sufficient if the powder paint supplied in regular amounts to the inlet port 79 of the injector 78 from the screw feeder 58 can be discharged through the hose 81 and the painting gun 82. An electropneumatic regulator may be provided in the air circuit to electrically control the air supply amount to a minimum value corresponding to the amount of discharge.
A sieve may be provided in the drop port 64 of the screw feeder 58 to improve the dispersibility of the powder paint. In Fig. 9, numeral 84 designates a height-adjustable base.
In the operation of this paint supply device, the pinch valve 53 is opened and closed at predetermined intervals so that the powder paint in the paint tank 51 will accumulate in the hopper 55 in predetermined amounts. The amount is detected by the level switch 56. Any abnormality of powder supply can be detected by electrically monitoring the opening and closing of the pinch valve 53 and the time taken until the powder reaches the level switch 56.
Namely, if clogging should occur somewhere in the powder supply line, since the power paint in the hopper 55 is not consumed, the time taken until the powder paint reaches the level switch 56 after opening the pinch valve 53 will become shorter than a monitoring cycle time. If the powder supply line from the paint tank 51 to the hopper 55 should fail, the time taken until the powder paint reaches the level switch 56 will become longer than the monitoring cycle time. If the time is out of the range of monitoring cycle time, the line is stopped on the assumption that it has failed.
Any excess air in the powder paint supplied into the hopper 55 is spontaneously expelled while being accumulated. The powder paint in the hopper 55 is fed out at a constant rate through the discharge port 60 by the screw feeder 58. By this push-out force, the spring 69 is compressed and the lid plate 67 is opened, so that the powder paint pushed out through a gap between the lid plate 67 and the discharge port 60 will blow out. The powder paint blown out of the lid plate 67 and the discharge port 60 then hits the inner surface of the flow straightener 63 and is supplied at a constant rate into the inlet port 79 of the injector 78 through the drop port 64 and the chute 76.
The powder paint supplied into the injector 78 is then supplied by air through the hose 81 and discharged through the painting gun 82.
If the hose 81 is clogged with powder paint, the powder paint will flow over the inlet port 79 of the injector 78 and keep at the outlet 77 of the chute 76. The accumulation of the powder paint at the outlet of the chute 76 is detected by the sensor 3. This makes it possible to stop the painting line when abnormality is detected. Thus, production of defective articles can be minimized.
As described above, according to this invention, since powder paint can be supplied at a uniform rate into the injector, the amount of paint discharged through the painting gun can be kept uniform even if there is a slight pressure loss in the hose of the painting gun.
Since the amount of powder paint to be supplied into the injector can be changed by changing the revolving speed of the screw of the screw feeder, the discharge rate through the painting gun can be set to any desired value.

Claims

A paint supply device for an electrostatic powder painting device having a paint tank (51) for containing a paint powder and a painting gun (82) coupled to said paint tank through an injector (78) and a hose (81) wherein said paint supply device further comprises: (i) discharge means (54) for discharging the powder paint out of said paint tank; (ii) a hopper (55) for receiving the powder paint discharged by said discharge means; (iii) a screw feeder (58) provided in said hopper for feeding powder paint from said hopper to said injector, said screw feeder (58) comprising a screw (59) having a tip thereof protruding into a discharge port (60) of the hopper (55); (iv) a flow straightener (63) provided adjacent said discharge port (60) and having a drop port (64) in the bottom thereof; (v) a closure plate (67) for closing said discharge port (60) slidable in the axial direction of said screw, and (vi) biassing means (69) for urging said closure plate against said discharge port.
A paint supply device as claimed in claim 1, wherein said biassing means is a spring (69) housed in a spring housing (65) adapted to be kept at a positive pressure.
A fluidized type powder paint tank having a fluidizing chamber for fluidizing a powder paint and a storage chamber into which the powder paint in said fluidizing chamber is fed to keep it still, characterized in that discharge means for discharging said powder paint is provided in said storage chamber.
A paint supply device for an electrostatic powder painting device having a paint tank for containing a powder paint and a painting gun coupled to said paint tank through an injector and a hose, characterized in that said paint supply device further comprises discharge means for discharging the powder paint out of said paint tank, a hopper for receiving the powder paint discharged by said discharge means, and a screw feeder provided over said hopper, whereby the powder paint supplied at a uniform rate from said screw feeder is fed into said injector.
A paint supply device for an electrostatic powder painting device as claimed in claim 4, wherein said screw feeder comprises a casing provided in the lower side thereof with a discharge port, and a screw having a tip thereof protruding into said discharge port, said paint supply device further comprising a flow straightener provided adjacent said discharge port and having a drop port in the bottom thereof, a lid plate provided so as to be slidable in the direction of axis of said screw for closing said discharge port, and biasing means for urging said lid plate against said discharge port.
A paint supply device in an electrostatic powder painting device as claimed in claim 5, wherein said biasing means is a spring housed in a spring housing kept at a positive pressure.
A powder paint supply device having a powder paint tank, an outlet pipe connected to the lower part of said powder paint tank, a pinch valve provided on said outlet pipe for closing the flow path by supplying air through an air supply pipe into said outlet pipe, characterized in that a branch pipe is connected to said air supply pipe, and to said outlet pipe at its portion located upstream of said pinch valve.